1. Field of the Invention
The present invention relates to an image capturing apparatus and a control method thereof.
2. Description of the Related Art
In an image captured by an image capturing apparatus such as a digital camera, an object image sometimes blurs when, for example, the hand of a user holding the camera body swings at the time of image capturing to cause a so-called camera shake. Most digital cameras have a function of correcting a blur of an object image that appears on an image capturing screen owing to vibrations acting on the camera body.
Conventionally, optical image blur correction processing and electronic image blur correction processing have been known as image blur correction processing. In optical image blur correction processing, a vibration of the camera body is detected by an angular velocity sensor or the like, and an anti-vibration lens in an imaging optical system is moved to change the optical axis direction of the imaging optical system. Accordingly, an image formed on the light receiving surface of an image sensor is moved to correct the image blur. In electronic image blur correction processing, image processing is performed on a captured image to pseudo-correct an image blur.
A shake signal output from the angular velocity sensor contains, for example, a signal arising from a camera operation intended by the user, such as a panning operation, in addition to a signal arising from a vibration to be corrected, such as a camera shake. If the anti-vibration lens is simply driven based on a shake signal, image blur correction is performed even on a large shake such as a pan or tilt. However, it is not preferable to perform image blur correction processing upon the panning or tilting operation. This is because the anti-vibration lens may exceed a drivable range, or an image swing (swing-back) occurs after panning or tilting, and the camera operation or video becomes unnatural.
To solve this, there is known swing-back correction in which, when it is determined that a shake signal output from the angular velocity sensor arises from the panning or tilting operation, image blur correction is stopped, and the anti-vibration lens is returned to the center (reference position having a displacement amount of 0) of the movable range and is stopped.
At the end of the panning or tilting operation, a shake signal does not become strictly 0, but gradually comes close to 0 owing to, for example, a residual signal from a high-pass filter (HPF) or integrator in a detection signal processing system upon an abrupt change of the angular velocity of the camera. When image blur correction is restarted, the anti-vibration lens greatly moves in accordance with the shake signal, causing a swing-back of an image.
As a technique for preventing the swing-back, Japanese Patent Laid-Open No. 2006-113264 has disclosed image blur correction in which the cutoff frequency of an angular velocity signal processing system filter is changed stepwise at the end of the panning operation. Japanese Patent Laid-Open No. 2011-118073 has disclosed a method of performing velocity control corresponding to the angular velocity for driving of an anti-vibration lens without using an HPF or LPF (integrator) having an ultralow cutoff frequency in an angular velocity signal processing system filter, which serves as the cause of a swing-back. Japanese Patent Laid-Open No. 2010-004370 has disclosed a technique of correcting a shake by a shake correction lens based on a shake signal detected by an angular velocity sensor, and correcting a shake by electronic vibration isolation based on an image blur signal of a low-frequency component. Even if a large shake is generated by the panning or tilting operation or the like, the driving range of the anti-vibration lens can be satisfactorily ensured.
In the method described in Japanese Patent Laid-Open No. 2006-113264, vibration isolation immediately after the panning or tilting operation becomes weak.
In the method described in Japanese Patent Laid-Open No. 2011-118073, the anti-vibration lens is centered by position control at all times other than exposure, and the anti-vibration performance is weakened with respect to the low-frequency component of a shake signal corresponding to a swing of the body or the like. When the offset of the angular velocity sensor or the temperature fluctuation is large, the anti-vibration lens quickly moves away from the center because there is no HPF. Thus, an expensive sensor such as a quartz gyroscope almost free from an offset or temperature fluctuation becomes necessary.
In the method described in Japanese Patent Laid-Open No. 2010-004370, the shake correction performance drops with respect to a low frequency at the time of exposure in which electronic vibration isolation cannot be performed.